Without a doubt one of the greatest upgrades you can make to your system is a power cord. There are a lot of hokey devices out there that may or may not work, but a power cable is not one of those. They work wonders.
Do power cords make a difference?
I have a fairly sophisticated Home Theater set up with top quality components and cabling. I also have a 5 year old female Rhodesian Ridgeback named Lola. Last week I changed just the power cords to my processor and DVD player. Now every time a dog barks or an animal makes its appropriate sound, Lola jumps off of the couch (it is no easy feat to get her off of the couch) and tries to attack the dog or animal making the sound. This did NOT happen before. Motto of the story, yes power cords make a difference that even my dog can tell!!!